In the present context, the term “fastening” is intended to refer to all methods for attaching elements to components, in particular attaching metal elements to metal components, for example by adhesive bonding, by forming, such as riveting, or by the union of materials, such as welding, including short-cycle arc welding. Short-cycle arc welding is frequently referred to as stud welding, even though studs are not the only article welded in this manner.
Stud welding is used primarily, but not exclusively, in automotive production. In this context, metal elements, such as metal studs with and without threads, eyes, nuts, etc., are welded onto the sheet metal of a vehicle body. The metal elements then serve as anchors or mounting elements, for example for attaching passenger compartment fittings, lines, wiring and the like, to the body metal. The metal elements may be welding studs that have a shank, and a head somewhat larger in diameter than the stud shank. The fastening system head described in the aforementioned document is characterized in that it has an elongated carrier, one end of which can be attached to a robot. At the opposite, free end of the carrier, a fastening tool is mounted such that it is rotatable about an axis of rotation extending transverse to the longitudinal extent of the carrier.
The feed mechanism feeds singled elements to a transfer station on the carrier. The fastening tool is rotated on the carrier such that the readied element can be taken by the holding device. Then the fastening tool is rotated into a fastening position and a fastening operation is carried out. In this context, the fastening tool preferably has a linear motor as the fastening drive device.
Since a control unit can be arranged in the region of the attachment end of the carrier, the free end of the carrier with the fastening tool can be designed as a relatively small structural unit. Accordingly, the fastening tool can even be moved through openings to inaccessible parts of the component. Prior to the actual fastening process, the fastening tool is rotated into a suitable fastening position in each case. The fastening system head is oriented with respect to the component by means of the robot.
Then a conventional stud welding process, preferably in the drawn arc method, can be carried out. In this method, the stud is first placed on the component by means of the fastening drive device. Then a pre-conduction electric current is switched on, which flows through the stud and the component. Next, the stud is raised with respect to the component by means of the fastening drive device (linear motor). An electric arc forms.
The system then switches to the welding current. The end faces of the stud and component opposite one another begin to melt as a result of the high welding current. Then the stud is lowered onto the component again so that the two melts combine. The welding current is switched off upon contact with the component and short-circuiting of the arc, or shortly beforehand. All the molten material solidifies, and the weld connection is established.
Then the holding device is removed from the welded stud. If the holding device has two elastically preloaded jaws laterally gripping the stud shank, removal can be accomplished in that the fastening tool is rotated on the carrier, so the holding device is pulled away laterally, so to speak. During the actual fastening process, the feed mechanism can make ready an additional element, which then will be picked up during the movement of the fastening system head to a next weld point by rotating the fastening tool toward the transfer station.